Effects of cigarette smoking on cortical thickness in major depressive disorder.

Findings of surface-based morphometry studies in major depressive disorder (MDD) are still inconsistent. Given that cigarette smoking is highly prevalent in MDD and has documented negative effects on the brain, it is possible that some of the inconsistencies may be partly explained by cigarette use. The aim of the current study was to examine the influence of cigarette smoking on brain structure in MDD. 50 MDD patients (25 smokers and 25 non-smokers) and 22 age, education, gender and BMI matched non-smoker healthy controls underwent structural magnetic resonance imaging. Thickness and area of the cortex were measured using surface-based morphometry implemented with Freesurfer (v5.3.0). The non-smoker MDD patients had significantly increased cortical thickness, including in the left temporal cortex (p < 0.001), right insular cortex (p = 0.033) and left pre- and postcentral gyrus (p = 0.045), compared to healthy controls. We also found decreased cortical thickness in MDD patients who smoked compared to non-smoking patients in regions that overlapped with the regions found to be increased in non-smoking patients in comparison to controls. Non-smoker MDD patients had increased surface area in the right lateral occipital cortex (p = 0.009). We did not find any region where cortical thickness or surface area significantly differed between controls and either smoker MDD patients or all MDD patients. The findings of the current study suggest that cigarette smoking is associated with cortical thinning in regions found to be increased in patients with MDD. However, these results should be considered preliminary due to methodological limitations.

Abnormal white matter integrity in synthetic cannabinoid users.

Synthetic cannabinoids have become increasingly popular in the last few years especially among adolescents and young adults. However, no previous studies have assessed the effects of synthetic cannabinoids on the structure of the human brain. Understanding the harms of synthetic cannabinoid use on brain structure is therefore crucial given its increasing use. Diffusion tensor imaging (DTI) was performed in 22 patients who used synthetic cannabinoids more than five times a week for at least 1 year and 18 healthy controls. Fractional anisotropy (FA) was significantly reduced in the cannabinoid group compared to controls in a cluster of white matter voxels spanning the left temporal lobe, subcortical structures and brainstem. This cluster was predominantly traversed by the inferior fronto-occipital fasciculus, inferior longitudinal fasciculus, fornix, cingulum-hippocampus and corticospinal tracts. Long-term use of synthetic cannabinoids is associated with white matter abnormalities in adolescents and young adults. Disturbed brain connectivity in synthetic cannabinoid users may underlie cognitive impairment and vulnerability to psychosis.

The effects of inhalant misuse on attentional networks.

Inhalant misuse among adolescents is poorly understood from a neuropsychological perspective. This study aimed to identify attentional deficits related to inhalant misuse measured with the Attention Network Test (ANT). We examined three groups: 19 inhalant users, 19 cannabis users, and 18 community controls. There were no group differences on the ANT measures of orienting, alerting, and executive control. However, compared to the cannabis and control groups, inhalant users demonstrated an increased rate of response errors in the absence of any reaction time differences. These differences may reflect a selective deficit in sustained attention or greater impulsivity in the inhalant group.

Longitudinal neuroimaging and neuropsychological changes in bipolar disorder patients: review of the evidence.

Longitudinal studies of biological domains in bipolar disorder (BD) are crucial in determining if such baseline changes are progressive. We reviewed reported studies of longitudinal brain structural/functional magnetic resonance imaging (MRI) and neuropsychological changes in BD through November 2012. Longitudinal brain structural MRI studies suggest cortical and subcortical abnormalities within networks subserving emotional regulation. There is evidence of neuroprogressive loss of gray matter volume in prefrontal and anterior cingulate cortex and the subgenual region, with less consistent findings in temporal and subcortical regions. Abnormal amygdala neurodevelopment is noted in adolescent onset BD and possible changes in hippocampus require further evaluation. The fewer reported longitudinal functional MRI studies suggest neurobiological changes in activation patterns involving fronto-limbic circuitry which relate to different illness phase and mood states. Early onset pediatric/adolescent BD may signify a more malignant course of illness in which extensive and executive neurocognitive deficits are found early and may persist, with some potential for improvement during remission and perhaps with treatment. Future studies should include larger samples, combine investigational modalities, incorporate genetic profiles, consider standardization of assessments and collaborative ventures across institutions, selection of more homogeneous subgroups and track neurobiological changes longer to clarify trajectories of changes.

Cingulate biochemistry in heroin users on substitution pharmacotherapy.

OBJECTIVE: High doses of opiate substitution pharmacotherapy are associated with greater treatment retention and lower illicit drug consumption, although the neurobiological bases of these benefits are poorly understood. Dysfunction of the anterior cingulate cortex (ACC) is associated with greater addiction severity and mood dysregulation in opiate users, such that the beneficial effects of substitution pharmacotherapy may relate to normalisation of ACC function. This study aimed to investigate the differential impact of methadone compared with buprenorphine on dorsal ACC biochemistry. A secondary aim was to explore the differential effects of methadone and buprenorphine on dorsal ACC biochemistry in relation to depressive symptoms. METHODS: Twenty-four heroin-dependent individuals stabilised on methadone (n=10) or buprenorphine (n=14) and 24 healthy controls were scanned using proton Magnetic Resonance Spectroscopy and compared for metabolite concentrations of N-acetylaspartate, glutamate/glutamine, and myo-inositol. RESULTS: (1) Methadone was associated with normalisation of dorsal ACC biochemistry (increased N-acetylaspartate and glutamate/glutamine levels, and decreased myo-inositol levels) in a dose-dependent manner; (2) buprenorphine-treated individuals had higher myo-inositol and glutamate/glutamine levels than methadone-treated patients in the right dorsal ACC; and (3) myo-inositol levels were positively correlated with depressive symptoms in participants stabilised on buprenorphine. CONCLUSIONS: These findings point to a beneficial role of high-dose methadone on dorsal ACC biochemistry, and suggest a link between elevated myo-inositol levels and depressive symptoms in the context of buprenorphine treatment.

White-matter abnormalities in adolescents with long-term inhalant and cannabis use: a diffusion magnetic resonance imaging study.

BACKGROUND: There is growing evidence that inhalants are neurotoxic to white matter, yet limited work has been conducted to investigate the neurobiologic effects of long-term exposure among adolescent users, despite inhalant use being most prominent during this developmental period. METHODS: We used diffusion tensor imaging to examine white-matter integrity in 11 adolescents who used inhalants, 11 matched cannabis users and 8 drug-naive controls. RESULTS: Although both groups of drug users had white-matter abnormalities (i.e., lower fractional anisotropy), abnormalities were more pronounced in the inhalant group, particularly among early-onset users. LIMITATIONS: The findings of this study should be considered in light of its small sample size, cross-sectional design and the complex psychosocial background of long-term inhalant users. CONCLUSION: White-matter abnormalities may underpin long-term behavioural and mental health problems seen in individuals with long-term inhalant use.